Walkthrough: Creating a Margin Glyph

Article
11/15/2016

Note

This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

You can customize the appearance of editor margins by using custom editor extensions. This walkthrough puts a custom glyph on the indicator margin whenever the word "todo" appears in a code comment.

Prerequisites

Starting in Visual Studio 2015, you do not install the Visual Studio SDK from the download center. It is included as an optional feature in Visual Studio setup. You can also install the VS SDK later on. For more information, see Installing the Visual Studio SDK.

Creating a MEF Project

Create a C# VSIX project. (In the New Project dialog, select Visual C# / Extensibility, then VSIX Project.) Name the solution TodoGlyphTest.
Add an Editor Classifier project item. For more information, see Creating an Extension with an Editor Item Template.
Delete the existing class files.

Defining the Glyph

Define a glyph by implementing the IGlyphFactory interface.

To define the glyph

Add a class file and name it TodoGlyphFactory.

Add the following using declarations.

using System.ComponentModel.Composition;
using System.Windows;
using System.Windows.Shapes;
using System.Windows.Media;
using System.Windows.Controls;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Editor;
using Microsoft.VisualStudio.Text.Formatting;
using Microsoft.VisualStudio.Text.Tagging;
using Microsoft.VisualStudio.Utilities;

Imports System.ComponentModel.Composition
Imports System.Windows
Imports System.Windows.Shapes
Imports System.Windows.Media
Imports System.Windows.Controls
Imports Microsoft.VisualStudio.Text
Imports Microsoft.VisualStudio.Text.Editor
Imports Microsoft.VisualStudio.Text.Formatting
Imports Microsoft.VisualStudio.Text.Tagging
Imports Microsoft.VisualStudio.Utilities

Add a class named TodoGlyphFactory that implements IGlyphFactory.

internal class TodoGlyphFactory : IGlyphFactory

Friend Class TodoGlyphFactory
    Implements IGlyphFactory

Add a private field that defines the dimensions of the glyph.

const double m_glyphSize = 16.0;

Const m_glyphSize As Double = 16.0

Implement GenerateGlyph by defining the glyph user interface (UI) element. TodoTag is defined later in this walkthrough.

public UIElement GenerateGlyph(IWpfTextViewLine line, IGlyphTag tag)
{
    // Ensure we can draw a glyph for this marker.
    if (tag == null || !(tag is TodoTag))
    {
        return null;
    }

    System.Windows.Shapes.Ellipse ellipse = new Ellipse();
    ellipse.Fill = Brushes.LightBlue;
    ellipse.StrokeThickness = 2;
    ellipse.Stroke = Brushes.DarkBlue;
    ellipse.Height = m_glyphSize;
    ellipse.Width = m_glyphSize;

    return ellipse;
}

Public Function GenerateGlyph(ByVal line As IWpfTextViewLine, ByVal tag As IGlyphTag) As System.Windows.UIElement Implements IGlyphFactory.GenerateGlyph
    ' Ensure we can draw a glyph for this marker.
    If tag Is Nothing OrElse Not (TypeOf tag Is TodoTag) Then
        Return Nothing
    End If

    Dim ellipse As Ellipse = New Ellipse()
    ellipse.Fill = Brushes.LightBlue
    ellipse.StrokeThickness = 2
    ellipse.Stroke = Brushes.DarkBlue
    ellipse.Height = m_glyphSize
    ellipse.Width = m_glyphSize

    Return ellipse

End Function

Add a class named TodoGlyphFactoryProvider that implements IGlyphFactoryProvider. Export this class with a NameAttribute of "TodoGlyph", an OrderAttribute of After VsTextMarker, a ContentTypeAttribute of "code", and a TagTypeAttribute of TodoTag.

[Export(typeof(IGlyphFactoryProvider))]
[Name("TodoGlyph")]
[Order(After = "VsTextMarker")]
[ContentType("code")]
[TagType(typeof(TodoTag))]
internal sealed class TodoGlyphFactoryProvider : IGlyphFactoryProvider

<Export(GetType(IGlyphFactoryProvider)), Name("TodoGlyph"), Order(After:="VsTextMarker"), ContentType("code"), TagType(GetType(TodoTag))>
Friend NotInheritable Class TodoGlyphFactoryProvider
    Implements IGlyphFactoryProvider

Implement the GetGlyphFactory method by instantiating the TodoGlyphFactory.

public IGlyphFactory GetGlyphFactory(IWpfTextView view, IWpfTextViewMargin margin)
{
    return new TodoGlyphFactory();
}

Public Function GetGlyphFactory(ByVal view As IWpfTextView, ByVal margin As IWpfTextViewMargin) As IGlyphFactory Implements IGlyphFactoryProvider.GetGlyphFactory
    Return New TodoGlyphFactory()
End Function

Defining a Todo Tag and Tagger

Define the relationship between the UI element that you defined in the previous steps and the indicator margin by creating a tag type and tagger, and exporting it by using a tagger provider.

To define a todo tag and tagger

Add a new class file to the project and name it TodoTagger.

Add the following imports.

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Tagging;
using Microsoft.VisualStudio.Text.Editor;
using Microsoft.VisualStudio.Text.Classification;
using Microsoft.VisualStudio.Utilities;

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel.Composition
Imports Microsoft.VisualStudio.Text
Imports Microsoft.VisualStudio.Text.Tagging
Imports Microsoft.VisualStudio.Text.Editor
Imports Microsoft.VisualStudio.Text.Classification
Imports Microsoft.VisualStudio.Utilities

Add a class named TodoTag.

internal class TodoTag : IGlyphTag

Friend Class TodoTag
    Implements IGlyphTag

    Public Sub New()
        MyBase.New()
    End Sub
End Class

Modify the class named TodoTagger that implements ITagger<T> of type TodoTag.

internal class TodoTagger : ITagger<TodoTag>

Friend Class TodoTagger
    Implements ITagger(Of TodoTag)

To the TodoTagger class, add private fields for an IClassifier and for the text to find in the classification spans.

private IClassifier m_classifier;
private const string m_searchText = "todo";

Private m_classifier As IClassifier
Private Const m_searchText As String = "todo"

Add a constructor that sets the classifier.

internal TodoTagger(IClassifier classifier)
{
    m_classifier = classifier;
}

Friend Sub New(ByVal classifier As IClassifier)
    m_classifier = classifier
End Sub

Implement the GetTags method by finding all the classification spans whose names include the word "comment" and whose text includes the search text. Whenever the search text is found, yield back a new TagSpan<T> of type TodoTag.

IEnumerable<ITagSpan<TodoTag>> ITagger<TodoTag>.GetTags(NormalizedSnapshotSpanCollection spans)
{
    foreach (SnapshotSpan span in spans)
    {
        //look at each classification span \
        foreach (ClassificationSpan classification in m_classifier.GetClassificationSpans(span))
        {
            //if the classification is a comment
            if (classification.ClassificationType.Classification.ToLower().Contains("comment"))
            {
                //if the word "todo" is in the comment,
                //create a new TodoTag TagSpan
                int index = classification.Span.GetText().ToLower().IndexOf(m_searchText);
                if (index != -1)
                {
                    yield return new TagSpan<TodoTag>(new SnapshotSpan(classification.Span.Start + index, m_searchText.Length), new TodoTag());
                }
            }
        }
    }
}

Private Function GetTags(ByVal spans As NormalizedSnapshotSpanCollection) As IEnumerable(Of ITagSpan(Of TodoTag)) Implements ITagger(Of TodoTag).GetTags
    Dim list As List(Of ITagSpan(Of TodoTag))
    list = New List(Of ITagSpan(Of TodoTag))()

    For Each span As SnapshotSpan In spans
        'look at each classification span \
        For Each classification As ClassificationSpan In m_classifier.GetClassificationSpans(span)
            'if the classification is a comment
            If classification.ClassificationType.Classification.ToLower().Contains("comment") Then
                'if the word "todo" is in the comment,
                'create a new TodoTag TagSpan
                Dim index As Integer = classification.Span.GetText().ToLower().IndexOf(m_searchText)
                If index <> -1 Then
                    list.Add(New TagSpan(Of TodoTag)(New SnapshotSpan(classification.Span.Start + index, m_searchText.Length), New TodoTag()))
                End If
            End If
        Next classification
    Next span

    Return list
End Function

Declare a TagsChanged event.

public event EventHandler<SnapshotSpanEventArgs> TagsChanged;

Public Event TagsChanged(ByVal sender As Object, ByVal e As Microsoft.VisualStudio.Text.SnapshotSpanEventArgs) Implements Microsoft.VisualStudio.Text.Tagging.ITagger(Of TodoTag).TagsChanged

Add a class named TodoTaggerProvider that implements ITaggerProvider, and export it with a ContentTypeAttribute of "code" and a TagTypeAttribute of TodoTag.

[Export(typeof(ITaggerProvider))]
[ContentType("code")]
[TagType(typeof(TodoTag))]
class TodoTaggerProvider : ITaggerProvider

<Export(GetType(ITaggerProvider)), ContentType("code"), TagType(GetType(TodoTag))>
Friend Class TodoTaggerProvider
    Implements ITaggerProvider

Import the IClassifierAggregatorService.

[Import]
internal IClassifierAggregatorService AggregatorService;

<Import()>
Friend AggregatorService As IClassifierAggregatorService

Implement the CreateTagger method by instantiating the TodoTagger.

public ITagger<T> CreateTagger<T>(ITextBuffer buffer) where T : ITag
{
    if (buffer == null)
    {
        throw new ArgumentNullException("buffer");
    }

    return new TodoTagger(AggregatorService.GetClassifier(buffer)) as ITagger<T>;
}

Public Function CreateTagger(Of T As Microsoft.VisualStudio.Text.Tagging.ITag)(ByVal buffer As Microsoft.VisualStudio.Text.ITextBuffer) As Microsoft.VisualStudio.Text.Tagging.ITagger(Of T) Implements Microsoft.VisualStudio.Text.Tagging.ITaggerProvider.CreateTagger
    If buffer Is Nothing Then
        Throw New ArgumentNullException("buffer")
    End If

    Return TryCast(New TodoTagger(AggregatorService.GetClassifier(buffer)), ITagger(Of T))
End Function

Building and Testing the Code

To test this code, build the TodoGlyphTest solution and run it in the experimental instance.

To build and test the TodoGlyphTest solution

Build the solution.
Run the project by pressing F5. A second instance of Visual Studio is instantiated.
Make sure that the indicator margin is showing. (On the Tools menu, click Options. On the Text Editor page, make sure that Indicator margin is selected.)
Open a code file that has comments. Add the word "todo" to one of the comment sections.
A light blue circle that has a dark blue outline should appear in the indicator margin to the left of the code window.